1. Technical Field
The invention relates to a method and a device for detecting magnetic fields, particularly for detecting the position of objects. Concretely, the invention relates to a method for detecting magnetic fields, particularly for detecting the position of objects, with a preferably oblong, soft-magnetic element, which is connected to electronics, with the impedance of the soft-magnetic material being measured via electronics. Furthermore, the invention relates to a device for detecting magnetic fields, particularly for detecting the position of objects, with a preferably oblong, soft-magnetic material, which is connected to electronics, with by the electronics the impedance (quality) of the soft-magnetic material being determined/measured, particularly for applying the method according to the invention.
Tasks for measuring positions need to be solved in numerous applications. In automation technology it is necessary to detect the position of objects in the processing sequence or to monitor moving machine parts. In the automotive field, particularly in motor vehicles, a plurality of movements and positions are monitored in or at the motor, the clutch, the transmission, body parts, etc. Similar applications also exist in the field of aeronautics, where in airplanes the position of flaps, doors, or landing gear is to be detected. Additionally, in the consumer field, e.g., in washing machines, the weight of the textiles is weighed via a position measurement.
2. Description of Related Art
Numerous solutions for these position measurement tasks have been described in literature, which operate with different physical measuring methods, such as sensitive, capacitive, inductive, optic, or also magnetic measuring methods. A particular class of such measuring methods includes magnetic methods, because here usually a magnet is fastened at the object to be measured (measuring object). Here, sensors represent a variant, in which the magnet is allocated to the sensor and the reaction of the measuring object is detected. Here, the measuring object must show magnetic features, though, particularly ferromagnetic features. These sensors have in common that the position of the measuring object is detected by a magnetic reaction, which is detected by a sensor. Here, magnetic sensors are particularly suitable at places where the movement of mobile objects through fixed bodies must be detected. By the extension of magnetic fields through non-magnetic materials, for example the position of pistons within cylinders can be measured, if it comprises a non-magnetic material, for example aluminum.
Such position sensors with magnetic measuring principles have been known for quite some time.
There are several different methods and materials, which can be used for measuring the relative position of a sensor in reference to a measuring object with an integrated magnet (permanent magnet and electromagnet).
Typical examples include Hall-sensors, magneto-resistive sensors (AMR, GMR, XMR), flux-gate sensors.
From DE 196 21 886 A1 a magnetic position measuring device is known to determine the relative position of two objects mobile in reference to each other using at least one flux-gate sensor for scanning a periodically magnetized measuring division with the division period, with the flux-gate sensor comprising at least one exciter coil and at least two sensor coils arranged around a soft-magnetic carrier body, arranged at certain distances from each other.
For large measuring ranges several flux-gate sensors with a linear carrier body are arranged parallel in reference to each other and produced in thin-film technology.
An interpolation unit is also provided, which operates according to the principle of amplitude evaluation of carrier-frequency signals.
From DE 10 2007 062 862 A1 a method is known for determining the position of a measuring object in reference to a sensor, with the sensor comprising a sensor coil impinged with alternating current, in which the permeability of a soft-magnetic material changes under the influence of a magnetic field. The magnetic field is generated by a permanent magnet allocated to the measuring object.
Reference is made to additional magnetic sensors according to prior art described in DE 10 2007 062 862 A1.
The sensors of prior art show disadvantages, though:
Flux-gate sensors used according to DE 196 21 886 A1 include an exciter and two receiver coils, with the magnetization of a soft-magnetic core being measured. The sensor according to DE 10 2007 062 862 A1 also includes a coil supplied with alternating current. Coils are relatively expensive components, because they are difficult to wind or, in case of coils printed or etched on circuit boards, set high demands to the precision of the printing or etching process. Another disadvantage of such sensors is the fact that coils or magnetic cores represent relatively large-volume parts. Thus, it is not possible with these principles to produce small, compact sensors which can also be used in restricted construction spaces.
Another disadvantage of the sensors of prior art is the fact that they measure primarily the strength of the magnetic field H. For example, in Hall-sensors of prior art there is a direct linear connection between the measuring signal, namely the Hall-voltage UH and the magnetic field H. Even in the magneto-resistive sensors the primary measuring signal is proportional to the magnetic field H. Thus, the magnetic field can be measured very well with these types of sensors. A serious disadvantage is given here, though, in that the magnetic field of a permanent magnet or an electromagnet is not reducing linearly with increasing distance from the magnet but shows an extremely non-linear (frequently exponentially) reducing parameter, which is known per se. Thus, any sensor comprising a linear parameter with regards to the magnetic field H is suitable to a limited extent only for detecting the position of a measuring object comprising a magnet. In technology it is particularly advantageous to obtain a signal which is linearly dependent on the desired size, in this case the position or the distance of a measuring object, because then any expensive linearization or calibration can be omitted. In order to obtain an approximately linear signal in spite of non-linear parameters frequently the measuring range is limited so that from the non-linear parameter only a small segment is utilized, in a first approximation sectionally linear. However, this method drastically restricts the measuring range available.